Tectonic Features in Western Arabia Terra and Their Implications for the Exomars 2022 Rover Landing Site

52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548) 1234.pdf

TECTONIC FEATURES IN WESTERN ARABIA TERRA AND THEIR IMPLICATIONS FOR THE EXOMARS 2022 ROVER LANDING SITE. S. Z. Woodley*, P. Fawdon, M. R. Balme, D. A. Rothery, and E. Favaro. The Open University, Walton Hall, Milton Keynes, United Kingdom. *[email protected]

Introduction: Oxia Planum, the landing site of Our study site is a 1 million km2 area centered on the ExoMars Rosalind Franklin rover [1], is located in Kilkhampton crater in Oxia Planum (Fig 1b). Tectonic transitional terrain between the Arabia Terra highlands features occur across the region including near the Ex- and the Chryse Planitia lowlands (Fig 1). Recent work oMars rover landing site and in the channel floors of shows that Arabia Terra hosted extensive river systems Ares, Coogoon, and Mawrth Valles. during the Noachian period (> 3.7 billion years ago) [2, Wrinkle ridges are the most common tectonic 3]. In our study area in west Arabia Terra (Fig 1b), the structures in the study area; these are curvilinear topo- fluvial landscape has been exhumed from beneath graphic highs that are morphologically complex and younger sedimentary terrains [e.g. 4] while also being varied [e.g. 5; Fig 2b]. Wrinkle ridges generally consist modified by tectonism. The impact of tectonism, on of a broad rise, a superposed ridge, and a small crenu- both regional and global scales, on the geological his- lation. These three elements are commonly described tory of west Arabia Terra is poorly understood; it could as first, second, and third order ridges respectively [6], have implications for palaeohydrology and the eleva- but any one of these elements can be absent in an indi- tion of proposed shoreline features. To provide con- vidual wrinkle ridge. The accepted interpretation of straints on the tectonic evolution of the region, we wrinkle ridges as tectonic features that formed by have constructed a preliminary map of tectonic fea- compressional faulting and folding [7] is based on ob- tures in west Arabia Terra (Fig 1) and analyzed their servations of vertical offset across ridges, ridges trace- orientations. able along their length into fault scarps (Fig 2b), offset of pre-existing craters, and comparison to terrestrial a) b) analogs [e.g. 6, 7].

a) b)

Minor ridge Fig 2b

Wrinkle ridge cutting mound Scarp Fig 2a

Figure 1. a) Global MOLA topographic map showing

location of study area in west Arabia Terra. b) Map of Figure 2. Example of various morphologies of tectonic tectonic features (red) in the study area (white circle), features in study area. a) Minor wrinkle ridge and on a geological base map [12]. The landing “ellipse” scarp-like ridge on the floor of Ares Vallis. b) Major of the ExoMars rover in Oxia Planum is shown in blue. wrinkle ridge in Chryse Planitia. (CTX images) 52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548) 1234.pdf

Methods: Fig 1b shows a preliminary map of tectonic features in the study area. The extent of the study area was chosen to include both highland and lowland terrain as well as the three previously mentioned Val- les. At this stage of the study, we have only digitized the ‘crests’ of the tectonic features. We digitized features at a scale of 1:50,000 using 6 m/pixel Context Camera (CTX) images [8], 100 m/pixel Thermal Emis- sion Imaging System (THEMIS) daytime infrared images [9], and 463 m/pixel gridded topographic data from the Mars Orbiter Laser Altimeter (MOLA) [10]. In order to account for illumination bias and to prevent east-west oriented ridges being overlooked, we also used High Resolution Stereo Camera (HRSC) [11] Figure 3. Rose diagram of the bidirectional orienta- hillshades constructed using multiple sun angles. tions of 500 m long sections (n = 78,036) of the wrin- To analyze the orientations of the tectonic fea- kle ridge crests in the study area. Axes represents seg- tures, we subdivided each ridge into 500 m long sec- ment count for each orientation. tions. For each 500 m section, we measured bidirec-

tional orientations, omitting sections <500 m. The bidi- Conclusion: We present preliminary findings of a rectional orientations of the 500 m sections are shown tectonic mapping survey in western Arabia Terra, per- in a rose diagram in Fig 3. formed CTX images. We suggest that multiple phases

of tectonic activity were responsible for the widespread Observations: We have identified numerous wrin- tectonic deformation. The predominantly north-south kle ridges in western Arabia Terra, with a combined orientation of the tectonic features is in line with ex- length of ~20,000 km. Our map shows that tectonic pected global trends. features occur across the highland-lowland transition

region and deform geomorphic units of all ages (Fig 1; Acknowledgments: We gratefully acknowledge [12]). However, the features appear to be predominant- funding from STFC grant ST/V50693X/1 and the ly concentrated in Noachian Plains units and Transition Open University STEM Faculty (SZW), and UK Space units. Fig 3 shows that the bidirectional orientation of Agency ST/R001413/1 (PF, MRB). wrinkle ridges is predominantly north-south trending;

East-west trending wrinkle ridges are approximately a References: [1] Vago, J.L. et al. (2017) Astrobio- factor of three less common. logy, 17, pp. 471-510. [2] Davis, J.M. et al. (2016)

Geol., 44, pp. 847-850. [3] Fawdon, P. et al. (2019) Interpretation: We suggest that the occurrence of LPSC abstract, LPI Contrib. No. 2132. [4] Quantin- tectonic features in units of all ages, coupled with the Nataf, C. et al. (2020; in press) Astrobiology. [5] heterogenous distribution of features across units, indi- Strom, R.G. (1972) Mod. Geol., 2, 133-157. [6] Wat- cates that multiple phases of tectonic activity occurred. ters, T.R. (1988) JGR: Solid Earth, 93, 10236-10254. This is in agreement with [3], who propose that there [7] Plescia, J.B. and Golombek, M.P. (1986) Geol. have been multiple episodes of tectonic and aqueous Soc. Am. Bull., 97.11, 1289-1299. [8] Malin M.C. et al. activity. We do not yet draw conclusions about the (2007) J Geophys Res, 112,1-25. [9] Christensen, P.R., relationship between fluvial and tectonic features, , as et al. (2004) Space Sci. Rev. 110, 85–130. [10] Smith, further study is required to determine their relative D. E., et al. (2001) J. Geophys. Res., 106, 23689– ages. 23722. [11] Neukum, G. and Jaumann, R. (2004) ESA Our observations of predominantly north-south Special Publication, 1240, 17–35. [12] Tanaka K.L. et trending tectonic features in west Arabia Terra are al. (2014) USGS Scientific Investigations Map 3292. broadly in line with expected trends of Tharsis-related [13] Watters, T. (1993) J Geophys Res, 98, 17049- tectonism in Mars’ western hemisphere [e.g. 13]. This 17060. shows that the small scale features similarly conform to the global tectonic stress regime. We have not yet explored the possible contribution of basin related stresses or stresses related to the dichotomy boundary.